Melamine process



2,833,765 Patented May 6, 1958 lVlEL 1 PROCESS Carroll A. Hochwalt, Clayton, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application August 15, 1956 Serial No. 604,070

3 Claims. (Cl. 260-2495) Example 1 To a 300-cc. rocker-type autoclave there was charged 44 g. of ammonium cyanide and 32 g. of sulfur. The ammonium cyanide had been previously prepmed by passing gaseous ammonia over liquid hydrogen cyanide until the white solid ammonium cyanide was formed. The autoclave was sealed at room temperature and it was then heated for about 2% hr. under the autogenously developed pressure of 225 p. s. i. g. to a temperature of about 340 C. At the end of the reaction period, the autoclave was cooled and vented. The reaction product was dissolved in hot water (100 C.) and filtered while hot to remove the water-insoluble materials. Enough sodium hydroxide was added to the filtrate to make a 10% caustic solution. This solution was cooled in an ice bath whereby the melamine was crystallized. The melamine crystals were then separated and dried. The

melamine product was identified both by infrared analysis and melting point. It melted at 347 C. as compared to 349 C. for an authentic sample of melamine and in a mixed melting point determination the melting point of the authentic melamine sample was 346 C.

It is to be understood that substantial variation may be made from the specific conditions set forth in the example without departing from the scope of the invention. For example, the ammonia and hydrogen cyanide 50 have ammonia present in excess to prevent decomposition of the melamine. mole ratio from 1:20 to 20:1 respectively may be used although practical considerations make it preferable to 5 maintain the mole ratio of hydrogen cyanide to ammonia in the range from 1:1 to 1:10. The quantity of I sulfur to be used is best related to the quantity of hydrogen cyanide employed. Equimolecular quantities a of these two reactants are satisfactory although slight excesses of sulfur are preferred. The sulfur may be employed in greater excess although too large an excess is to be avoided.

The temperature is not limited to 340 C. but may vary in the range from about 200 C. to about 450 C. with The pressure can also be varied considerably. It can be as low as 200 p. s. i. g. and as high as 2000 p. s. i. g. or even higher.

The reaction time required will vary with the temperature and can range from a few minutes to 8-10 hours or longer. At a temperature of about 300350 C., the

reaction is complete in approximately one hour, whereas at lower temperatures several hours are required.

Either batch or continuous processes are feasible. The product melamine may also be recovered from the reaction mass by various other means such as sublimation for example.

What is claimed is:

1. A method for the preparation of melamine which comprises heating together ammonia, hydrogen cyanide, and sulfur at a temperature in the range from 200 to 450 C. and a pressure in the range from 200 to 2000 p. s. i. g.

2. A method for the preparation of melamine which comprises heating together ammonia, hydrogen cyanide, and sulfur in a closed reaction zone at a temperature of about 340 C. and under autogenously developed pressure.

3. The method of claim 2 in which the mole ratio of 40 ammoniazhydrogen cyanidezsulfur is 1:1:1.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS France Dec. 31, 1931 Germany Aug. 17, 1932 OTHER REFERENCES Chemical Abstracts, vol. 38, p. 6075 (1944). stract of Klempt Gluckauf, vol. 79, pp. 520-522 (1943)). Jacobson, Chemical Markets, vol. 29, p. 365 (1931).

Beilsteins Handbuch der Organischen Chemie, vol'. 26 (4th ed. 1937 printing), p. 245 (Preparations of malamine).

Any hydrogen cyanide-ammonia temperatures in the range from 300- 0 being preferred.

Klempt July 16, 1935 Marsh Sept. 18, 1951 

1. A METHOD FOR THE PREPARATION OF MELAMINE WHICH COMPRISES HEATING TOGETHER AMMONIA, HYDROGEN CYANIDE, AND SULFUR AT A TEMPERATURE IN THE RANGE FROM 200 TO 450*C. AND A PRESSURE IN THE RANGE FROM 200 TO 2000 P. S. I. G. 